Electric circuit timer - How works electrical panel installation & circuit timer? It's a distribution board that ensures the safe distribution of the strong currents of all electrical points of the house.

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A back-and-forth circuit is an electrical circuit which makes it possible to switch off or switch on a light or any other electrical appliance from two switches, for example a switch at each end of a corridor for the same light lighting

The principle of the switch back and forth is to be able to control the switching on and off of one or more lamps in the same room from different locations. It is not the switch itself that is said back and forth but the electrical assembly. It is designed to be able to control the same circuit from two separate switches.
This device is recommended for corridors or rooms with multiple entrances.